[WolfPlayer]

I have heard it from a few people that it is totally cool to remove the rear O2 sensor on a Cobb Stage 2 so that you can utilize that location for a wideband. I have my wideband in the bung located on the APS high flow turbo outlet, aka HFTO (downpipe for those not familiar with the APS). This puts the wideband very close to the turbo and thus, the wideband gets REALLY hot. Such extreme heat decreases the wideband's longevity. Fast forward to yesterday when I was replacing all the gaskets in my TBE due to what I thought was a leak (turned out not to be). Anyhow, PERFECT time for me to remove the wideband from the APS HFTO and put it in the rear location. Cool. So, I completely removed the rear O2 sensor, taped the plug, and relocated my wideband to that rear location. Started the car and drove it around. No CELs - wideband reads normal - car feels fine. Woohooo! ... .. . or so I thought. Brought up the realtime data view and observed the stock AFR and my wideband AFR. Whoa. This is weird. Becomes very apparent that the ECU doesn't appear to be shooting for 14.7 anymore. Rather, it seems to be shooting for slightly richer ... 14.4-14.5 or so. Furthermore, when you let off the gas the AFR goes rich to ~13.5 and stays there. Very weird. I remembered a post by R4ND0M_AX4 awhile ago and he had these exact same conditions (http://www.wrxforum.com/cgi-bin/ulti...;f=14;t=000043). I thought it was weird at the time and never was able to reproduce it, and therefore, forgot about it. Well, I just reproduced it. Yick.

So, this morning I put the wideband back where it was and hooked the rear O2 sensor back up. Everything went back to normal. AFRs focused at 14.7 and when letting off the gas it did not go to 13.5AFRs. Yay!

Moral of the story, don't unhook the rear O2 sensor. Apparently there is some trigger in the code that will target different AFRs if this sensor is unplugged.

t

[daemon]

Interesting. I was comptemplating doing this recently. Maybe I won't now.

[WolfPlayer]

R4ND0M_AX4 confirmed that he was experiencing these symptoms with the rear O2 sensor disconnected.

Don't disconnect your rear O2 sensor.

t

[jays05]

Interesting. I'd love to hear something from Chrisitian @ Cobb on this one.

[R4ND0M_AX3]

Yuck.

[smurfm3]

It is my understanding that the rear oxygen sensor is used to trigger a CEL light that pertains to emissions. I am not aware of any issues with removing the rear O2 besides the Check Engine Light you will trigger, but I could be wrong. I have no experience with the AP; I only have experienced this using the stock ECU.

[WolfPlayer]

Originally Posted by smurfm3

It is my understanding that the rear oxygen sensor is used to trigger a CEL light that pertains to emissions. I am not aware of any issues with removing the rear O2 besides the Check Engine Light you will trigger, but I could be wrong. I have no experience with the AP; I only have experienced this using the stock ECU.

Well, simply put, you are now aware of a new issue

t

[jays05]

Did you try leaving your wideband in the front location, and removing/plugging the rear o2? That would tell us if the ecu is targeting a different afr, or if your wbo2 just reads a little differently when moved to the back port (perhaps due to a temp drop or a cat).

[R4ND0M_AX3]

I also wonder is it the lack of an O2 sensor or is the fact that the CELs are 'disabled' that is causing the condition we both are seeing?

I don't think the placement a foot or two further down the pipe would change the reading. But it's good science to test like mentioned.

Wolf, do you have any datalogs of before and after that show what the stock front sensor was reading?

[reid-o]

Originally Posted by R4ND0M_AX3

I also wonder is it the lack of an O2 sensor or is the fact that the CELs are 'disabled' that is causing the condition we both are seeing?

I don't think the placement a foot or two further down the pipe would change the reading. But it's good science to test like mentioned.

Wolf, do you have any datalogs of before and after that show what the stock front sensor was reading?

This is very interesting. What are your immediate trims at when the car is reading 13.5?

I'm curious if the ECU is really hunting for a new A/F or if the reading downstream is just that much of a difference.

[WolfPlayer]

Originally Posted by jaygoesfast

Did you try leaving your wideband in the front location, and removing/plugging the rear o2? That would tell us if the ecu is targeting a different afr, or if your wbo2 just reads a little differently when moved to the back port (perhaps due to a temp drop or a cat).

Jay - I am confident this is not the problem because I was logging BOTH the WB and the stock front Narrow Band. They both reported the same

t

[RainMaker]

Try this...

Put the post-cat 2nd 02 sensor up front in the HFTO and put the wideband in the rear...

Problem solved, right???

[smurfm3]

Originally Posted by WolfPlayer

Well, simply put, you are now aware of a new issue

t

So, do you know if this is a specific problem with the Cobb AP or does the stock ECU behave in the same way? Thanks in advance.

[WolfPlayer]

Originally Posted by smurfm3

So, do you know if this is a specific problem with the Cobb AP or does the stock ECU behave in the same way? Thanks in advance.

I really don't think this has anything to do with the AP. Cobb deletes the codes. However, if the ECU has logic based off of something to do with the stock rear O2 then this will still be in affect unless they have actually sought out these routines and disabled them.

t

[WolfPlayer]

Originally Posted by RainMaker

Try this...

Put the post-cat 2nd 02 sensor up front in the HFTO and put the wideband in the rear...

Problem solved, right???

Almost Another reason I didn't want to use the HFTO was because the sensor is mounted on the side pointing toward the tranny. I wanted to clear out that clutter. But, you make a great point I would just need to extend the wires for the stock rear O2. I don't think I will follow this approach ... but, you never know. It really is a good idea.

t